The present invention relates to an axle boot for joint sealing, in particular on the drive train of motor vehicles, that includes a substantially axisymmetric bellows, which is designed as a single piece with a connecting collar, and compensating pieces attached to and distributed over the connecting collar for the purpose of adapting to an external contour of a joint housing, a contour that includes a plurality of radial recesses.
Axle boots of this type are typically used to seal off joints in the drive train of motor vehicles, joints whose joint housing has an external contour that includes a plurality of radial recesses. Since three radial recesses are usually provided on the circumference, the result is a three-lobe external contour that is also described as trilobe-shaped, which is at the same time the interface to the axle boot, which is usually fastened by clamps. The sealing of the joint area is necessary in order to keep dirt and moisture away from the joint and to preserve the grease filling in the joint.
For the purpose of adapting the connecting collar of the bellows on to the non-axisymmetric external contour of the joint housing, it is known in the case of axle boots manufactured from elastomers by the injection-molding method to provide enlargements in the connecting collar that act as compensating pieces and compensate for the radius differences of the external contour of the joint housing so that a circular clamp can be used for clamping purposes.
In this case, pronounced undercuts are formed on the inside at the transition from the connecting collar to the bellows. The elastomer material that is used makes easy demolding possible, in spite of these pronounced undercuts, since it has sufficient reversible extensibility. This manufacturing method, however, is no longer possible if the axle boot is to be manufactured from a thermoplastic copolyester (TPE). A molding having such pronounced undercuts would be destroyed during demolding since it does not withstand the necessary extensions. In addition, the formation of great wall thickness differences in thermoplastic moldings requires long cooling times in the mold and results in sink marks or the formation of voids.
In order to avoid these difficulties, the connecting collar for a known axle boot (European Patent Application EP 0 924 450 A2) is cylindrical in design. An annular insert that is surrounded by the connecting collar is provided for the purpose of adapting to the joint housing's external contour, which is provided with radial recesses. This insert has a plurality of projections that protrude into the inside and fit into the radial recesses of the joint housing. The axle boot can be manufactured relatively easily because the connecting collar, in particular, has a constant wall thickness and no undercuts are formed that would be a hindrance during demolding. Disadvantageous, however, is the fact that the bellows or at least its connecting collar must be reheated in a second manufacturing step in order to create the bond with the insert. This has a disadvantageous effect on strength and geometry due to molecule rearrangement. In addition, there is another joint between the connecting collar and the insert that has no useful function but must also be designed so that it seals.
That type of joint is avoided in an axle boot described in European Patent Application EP 0 915 264 A2, through the formation, in a single piece, of compensating pieces on the inside of the connecting collar that fit into the radial recesses in the joint housing. The known axle boot is manufactured in a combined injection blow molding process that makes an automated manufacturing run possible. The compensating pieces must be reinforced by radial webs in order to transfer the clamping force for the purpose of connecting the axle boot to the joint housing. The necessary optimization of wall thickness distribution makes any changes in the compensating pieces complicated and expensive because the injection-molding mold has to be changed for this purpose.